Molding of open-cell soft polyurethane foam is conventionally performed by either batch or continuous processing. Existing batch systems for performing molding of open-cell soft polyurethane foam introduce a relatively slow reacting polyol and isocyanate liquid mixture into the mold from locations either above or below the mold as is more fully described below. After such introduction into the mold, the liquid mixture of polyol and isocyanate expands upon foaming to fill the mold with "one age of foam" as compared to "different age of foam" which results with continuous molding of open-cell soft polyurethane foam. Such continuous molding provides mixing of the polyol and isocyanate over an injection time period that varies depending upon how much foam is required and, for larger volumes, the initially mixed mixture is older than the finally injection mixture such that the ability of the expanding foam to completely fill the mold with a uniform consistency is adversely affected.
Batch type systems for molding of open-cell soft polyurethane foam as mentioned above provide a liquid mixture of polyol and isocyanate that eliminates the "different age of foam" problem involved with continuous systems. As such, the foam can more readily expand to completely fill the mold and thereby provide a superior product. However, there are still problems that result with existing batch type systems as described below.
Prior art batch type systems for supplying the liquid mixture of polyol and isocyanate to the mold from above have previously been of two types. In one type such as disclosed by U.S. Pat. No. 2,649,620 Miller and U.S. Pat. No. 4,260,355 Rohrig et al, a mixing chamber with an open bottom is positioned within the mold so that the mold provides a floor that closes the bottom of the mixing chamber and permits the introduction of the polyol and isocyanate for mixing by a mixer inserted from above. Lifting of the mixing chamber then allows the liquid mixture to be distributed throughout the mold for eventual foaming and concomitant expansion that fills the mold. The other type of top feed batch type system utilizes a mixing chamber that is supped above the mold and has a lower openable door such that polyol and isocyanate introduced into the closed mixing chamber for mixing by a mixer that is introduced from above can subsequently be released as a liquid mixture into the mold upon opening of the door whereupon the liquid mixture spreads through the mold in preparation for the foaming and concomitant expansion that fills the mold.
Prior batch type systems for batch molding open-cell soft polyurethane foam that is supplied into a mold from below incorporate a mold mixing chamber within the lower mold extremity or floor. A piston that closes the mixing chamber is movable vertically by a suitable actuator. Positioning of the piston in a lower position permits the polyol and isocyanate to be introduced into the mixing chamber for mixing by a mixer that is inserted into the mixing chamber from above. After the mixing, the piston moves the liquid mixture upwardly such that it is capable of filling the lower extremity of the mold in preparation for foaming and concomitant expansion that fills the mold. Such a mold construction is relatively expensive to produce since each mold must incorporate the piston/actuator construction associated with the mixing chamber.
With each of the types of batch molding systems described above, the time required to perform the mixing and transfer the liquid mixture of polyol and isocyanate to the mold necessitates that the mixture have a relatively slow reaction time such as on the order of about three to six minutes or more before foaming and concomitant expansion takes place. As such, the polyol cannot be highly activated with catalyst since the foaming and expansion would than be too fast to permit the transfer of the liquid mixture into the mold for distribution prior to the foaming and concomitant expansion that fills the mold. Also, the polyol and isocyanate must be at ambient temperature of approximately 70.degree. Fahrenheit because the small amount of catalyst which may be utilized tends to go to a gas state at temperatures over the ambient temperature of 70.degree. Fahrenheit and the balance of components is thus varied by that change such that uniform reaction cannot take place. Rather, the heat necessary to initiate the reaction must be provided by heating of the mold to approximately 180.degree. Fahrenheit which necessarily makes such conventional batch molding processes more difficult and expensive to be performed than would be the case without such mold heating.
In view of all of the problems discussed above, batch type molding of open-cell soft polyurethane foam has only been commercially used with relatively large foam products and with open mold or free rise molds wherein the upper extremity of the mold is defined by a movable mold member that provides shape to the upper foam surface but is easily moved upwardly so that the foam can freely expand upon foaming.
Additional prior art references noted in connection with the investigation conducted with respect to the present invention includes: U.S. Pat. No. 3,268,635 Krauss et al which discloses a plastic material having a foaming agent that is injected from an extruder into a mold cavity under pressure such that no foaming takes place until there is subsequent heating of the mold; U.S. Pat. No. 4,717,518 Cavender which discloses a mold that is filled with a high resiliency polyurethane foam that is exposed to atmospheric pressure at a time during the cure cycle such that the polymer strength is sufficient to contain the internal cell pressures which are greater than atmospheric such that there is no collapsing of the foam cells; and U.S. Pat. No. 4,721,279 Oleszko et al which discloses a foam mold having a self-cleaning mold vent.